1. Field of the Invention
This invention relates to certain copolymer compositions containing free anhydride functionality. These copolymers are low molecular weight esterification products of a terminally ethylenically unsaturated compound and a polymerizable maleic anhydride and are polymerizable or curable by radiation such as ultraviolet, electron beam, and the like. The cured products of these novel compositions provide adhesion to a variety of substrates when present in conventional binder or coating systems and promote dispersion of inorganic compounds such as metal oxides, pigments and the like. Hence, the cured products based on the novel partial esters of the present invention are useful in radiation-curable inks, coatings and adhesives for a variety of substrates, such as paper, plastics, glass, metals and the like.
2. Description of the Prior Art
Irradiation as a method of curing free radical polymerizable compositions has a number of advantages over heat or ambient temperature curing, including: rapid cure at ambient temperatures; elimination of solvents together with the environmental problems associated therewith and the cost of their recovery; elimination of direct use of fossil fuels for curing and their polluting effects; capability of coating heat-sensitive substrates; obtainment of excellent physical and electrical properties of resulting products; and achievement of various cost savings by use of automation and high speed operation and high production. However, radiation curing at times introduces its own difficulties, such as in connection with formulation of compositions having varying degrees of viscosity and flow to permit commercially acceptable radiation curing, use of toxic components, and inhibition of curing by air contact. These difficulties may be substantially overcome by selective formulation of the radiation curable compositions, and hence, the selection of components of radiation curable compositions becomes critical if the advantages of radiation curing are to be realized and desirable useful commercial products obtained.
Radiation-hardenable coating compositions are well known in the art. Monomers typically used heretofore for such purposes include acrylic and methacrylic acid esters of various diols and triols, such as 1,6-hexanediol, diethylene glycol, 1,4-butanediol, trimethylopropane, pentaerythritol or glycerol, as well as alkoxylated, such as ethoxylated and propoxylated derivatives thereof. Representative of patents directed to radiation polymerizable compositions include U.S. Pat. Nos. 3,594,410 and 3,380,831 concerned with printing and thermal transfer reproduction elements, as well as U.S. Pat. Nos. 3,912,670; 4,025,548; 4,183,796; 4,243,500; 4,360,540; and 4,404,075, all of which are directed to coatings and adhesives. None of these patents disclose the type of monomers upon which the present invention is predicated.
Half esters of styrene maleic acid anhydride copolymers have previously been described in U.S. Pat. Nos. 3,536,461 and 3,342,787 for applications other than radiation curing. Also, electro-coating compositions containing styrene-maleic anhydride copolymers derived from low molecular weight copolymers of styrene and maleic anhydride are disclosed in U.S. Pat. Nos. 3,862,067 and 3,884,856. In addition, esters of such copolymers with unsaturated alcohols are disclosed in U.S. Pat. No. 3,825,430, as well as U.S. Pat. No. 4,401,793 concerned with production of actinic-light polymerizable esters and as reactive thickners in anaerobic compositions, respectively, prepared by reacting an anhydride-containing polymer with an excess of hydroxy-alkylacrylate or methacrylate, the esters of these patent disclosures are characterized as being free of unreacted anhydride groups. French Patent Publication No. 2,253,772 is concerned with production of styrene-maleic anhydride polymers which have been esterified by an unsaturated alcohol or by a polyol partially esterified with an unsaturated aliphatic acid so that it contains free hydroxyl groups. Finally, U.S. Pat. No. 4,293,636 relates to photopolymerizable compositions useful for processing printing circuit boards comprising a polyester, a half-esterified hydroxyalkylacrylate of a polybasic acid, vinyl monomer and initiator.